This invention relates in general to quality of service in telecommunications networks, and relates in particular to improving the quality of service in wireless networks.
Users of telecommunications networks expect to receive dependable and reliable levels of service for various kinds of communications on those networks. The term “quality of service” (QoS) is sometimes used as a measure of quality provided by a particular telecommunications network, and those skilled in the art will recognize that quality of service may refer to mechanisms for reserving or allocating hardware or software/logical resources for traffic flowing on a telecommunications network. The nature of those resources may depend on user variables, such as the nature of the traffic (for example, video teleconferencing) and the extent to which the particular kind of traffic may require at least a minimum level of quality when traveling across the network. Quality of service guarantees may be important in applications such as real-time streaming multimedia presentations, interactive applications or voice over IP (VOIP), as those applications often require a fixed bit rate and are delay sensitive.
For wireline telecommunications networks, quality of service can be successfully provided by building network capacity that exceeds predictable or maximum-expected traffic loads or by building a lesser network capacity and utilizing certain QoS mechanisms such as explicit resource reservation (e.g., IntServ, Integrated Services) or traffic marking with priority traffic treatment (e.g., DiffServ, Differentiated Services). The performance of such wireline networks is predictable relatively independently of events happening outside the network, unless such events result in physical damage to the network itself. The assumption is that the telecommunications network supports the applications using the wireline network, and that the network must be designed and operated to provide certain levels of quality of service required for the particular applications using the network.
Wireless networks, which rely on radio-frequency (RF) communications between one or more wireless devices and/or fixed radio sites, cannot provide a certain and predictable quality of service like wireline networks. Wireless connections are subject to external interference from unrelated transmissions, co-interference (e.g., from other mobile terminals, or other cells), multi-path changes in signal propagation, signal path changes due to movement of the wireless terminal, and other variable factors. These factors and changes are largely uncontrollable, usually additive, usually severe, and usually rapid. Traditional quality of service methods cannot hope to deal reliably with the changes inherent with wireless networks, or at least not at any economically-feasible level.
The difficulties in adapting QoS-sensitive applications to wireless network dynamics depends on the RF interface, where “RF interface” refers to the portion of the overall network that is truly wireless as well as the associated equipment and software, the “interface” terminology referring to the transition from the service provider's wire-line network portion to the radio or wireless network portion. A given quality of service usually requires a particular bandwidth, as well as possibly a minimum delay and/or minimum jitter, but bandwidth on any given wireless connection cannot be guaranteed because maximum available bandwidth is related to the received power of the RF signal. Received RF power varies greatly, and often rapidly, and often uncontrollably because of the above-mentioned factors including changes in RF path, RF channel, and motion- or time-dependent multi-path variations in signal travel. These large-magnitude and rapid changes in wireless networks, at the worst, cause the network to drop communication that the RF interface cannot support. That result is, of course, unsatisfactory to users of the wireless network and limits the successful adaptation of new applications that require a dependable quality of service for operating on a wireless network, especially where these new application and services are particularly sensitive to bandwidth, delay/latency, and/or jitter.
One approach to overcoming the foregoing problem is to modify the RF interface to be more stable. Such modification, in traditional practice, amounts to adding more cell sites to the RF network so as to increase the breadth and the depth of coverage for the RF network. That approach is extremely expensive and, furthermore, may present practical as well as political problems in obtaining approval to add cell towers in some areas. Moreover, even adding cell sites to a near-saturation level may not succeed in overcoming the problems inherent with RF signal propagation.
Another possible solution to the problem is doing something in the wireless network to partially compensate for the uncontrollable variations of the RF interface. However, the wireless network cannot generally accomplish this because the variations inherent in the RF interface are mostly uncontrollable, such that the variable aspects of the wireless network cannot be commanded or controlled to adapt or control other elements in the data network.